Conventionally, in medical facilities, comparative reading has been performed, in which a diagnosis is made with reference to disease cases (similar disease cases) in the past similar to the disease case of a medical image which is a diagnostic target, and a similar case image retrieval apparatus is utilized as an apparatus that retrieves medical images of similar disease cases.
Diffuse lung disease is one of the cases for which it is difficult for a diagnostic radiologist to make a diagnosis when performing comparative reading. Diffuse lung disease is a disease that causes the function in an extensive region of the lung to be impaired and an impaired portion appears as an abnormal shadow, and the disease has characteristics that the shape and distribution of the abnormal shadow are complicated and diverse. For this reason, diagnosis of diffuse lung disease is more difficult than cancer of a solitary pulmonary nodule, and it is important to retrieve medical images of similar disease cases.
To cope with this, for instance, Japanese Laid-open Patent Publication Nos. 2009-45121, 2007-275216, and 2007-286945 propose a method to retrieving a medical image of a similar case based on an image characteristic quantity which is calculated for the shape of abnormal shadows in regions in a diagnostic target medical image. Furthermore, Japanese Laid-open Patent Publication No. 2006-34585 proposes a method to retrieving a medical image having abnormal shadows at positions similar to the positions of abnormal shadows in a diagnostic target medical image.